The broad goal is to investigate the ways in which bilingualism affects children's cognitive and linguistic development. Four specific aims each examines a different aspect of competence. The first aim is to investigate the cognitive effects of bilingualism on executive processing and develop more precise descriptions of the relationship between selective attention, inhibitory control, response suppression, and task switching. Executive functions are the basis of all higher thinking, including planning, attention, and monitoring. The second aim is to examine the extent to which bilingualism affects children's development of higher cognitive abilities in spatial and mathematical domains. Both are crucial aspects of children's development and integrally related to school achievement. The results will help to identify the basic skills that underlie problem solving in these domains and point to an important academic consequence of bilingualism. The third aim is to examine the effect of bilingualism on language development, specifically in terms of semantic processing and literacy acquisition. It is well known that bilingual children control a smaller vocabulary in each language than their monolingual counterparts. The effect of this difference on psycholinguistic processing and higher language skills, such as literacy, needs to be examined in detail for these children. Literacy acquisition is multifaceted, depending on both cognitive and semantic abilities, suggesting a complex role for bilingualism in its development. The fourth aim is to isolate the factors that are correlated with bilingualism, such as social class, education, cultural expectations, and immigration, that may be accounting for the results rather than bilingualism per se. Monolingual and bilingual children have many different experiences, so it is essential to demonstrate that the relevant source of difference on these tasks is only the number of languages they speak. The research for all these aims will compare monolinguals and bilinguals matched on SES, working memory, and reasoning ability, on the dependent measure selected for each specific aim. All these outcomes relate to children's intellectual development and school success and will contribute to theoretical conceptions of the structure of these abilities. The results will be used to understand how language experience affects development for a specific group of children and how the plasticity of the mind is responsive to social and linguistic contingencies in the environment.